Sado Island

Sado Island (佐渡島, Sado(ga)shima; Japanese pronunciation: [sa.do.ɡaꜜ.ɕi.ma, -do.ŋaꜜ-]) is an island located in the eastern part of the Sea of Japan, under the jurisdiction of Sado City, Niigata Prefecture, Japan, with a coastline of 262.7 kilometres (163.2 mi). In October 2017, Sado Island had a population of 55,212 people. Sado Island covers an area of 854.76 km² (330.02 sq mi), and is the sixth largest island in Japan, excluding the disputed Southern Kurils. The shortest distance between Sado Island and Honshu is 32 km (20 mi). The highest peak on Sado Island is Mount Kinpoku, with an elevation of 1,172 m (3,845 ft).

The shape of Sado Island resembles the kanji character for ‘work’ (工) in Japanese or the letter ‘S’. The topography of the island can be roughly divided into three parts, the Ōsado range in the north, the Kosado range in the south, and the Kakakura plain with flat terrain in between. The Ōsado range area is higher in altitude, and the highest peak of Sado Island, Mount Kinpoku (1,172 m (3,845 ft) above sea level), is also located in this area. The coastline on the north side of Mount Sado is steep, and is a famous tourist spot, among which the Senkaku Bay is the most famous. The Kosado range has a relatively flatter terrain with Satsuma orange and tea trees growing there. Its highest peak is Mount Ōjiyama, with an elevation of 646 m (2,119 ft). The Nakakura Plain is a large plain in Japan's outlying islands and is also the agricultural area of Sado Island. On the west side of the Kuninaka Plain is Mano Bay, and on the east side is Ryōtsu Bay. The Kokufugawa River (also reads Konogawa River) flows through the Kuninaka Plain, with a total length of 19 km (12 mi), and flows into Mano Bay. Its watershed area accounts for 20% of Sado Island. Lake Kamo, the largest lake in Niigata Prefecture, is located at the eastern end of the Kuninaka Plain. Lake Kamo was originally a freshwater lake, and later turned into a lagoon after an opening built to the Sea of Japan. Oyster breeding flourishes in the lake. Part of Sado Island belongs to the Sado-Yahiko-Yoneyama Quasi-National Park.

Affected by the warm Black Current that passes through the Sado waters, the winter in Sado Island is warmer than that in Niigata Prefecture and with less snow. In summer, due to the influence of ocean, the temperature difference between day and night is smaller than that of Niigata Prefecture, and is cooler than that of Niigata Prefecture. However, the Aikawa area on the northwestern side of the Ōsado range are affected by the monsoon blowing from the northwest and the temperature is higher. Precipitation on Sado Island is mainly concentrated in the end of the East Asian rainy season and early winter, and there is less precipitation than in Niigata Prefecture. When the low air pressure and typhoons pass through the Sea of Japan, Sado Island often suffers from Foehn wind, raising the temperature sharply. Located at the junction of the warm and cold current, Sado City enjoys diverse plants and rich aquatic resources.

Because it is located at the junction of warm and cold currents, it is extremely rich in vegetation, making it an extremely rare vegetation area on the island where plants unique to both Hokkaido and Okinawa coexist. It is also blessed with a variety of marine products, such as dolphinfish, bonito, and bigfin squid that appear in warm currents, and yellowtail that appears in cold currents.

Due to the hundreds of thousands of years that have passed since it was isolated from Honshu island, endemic species such as the Sado hare, Sado mole, and Sado shrew can be seen.^{[citation needed]} Although they are now extinct, there was a population of wild boars that was genetically separated from the population of Honshu for hundreds of thousands of years.^{[citation needed]} The Japanese weasel is said to have been re-introduced after becoming locally extinct.

Sado Island was originally connected to Honshu, but it separated from Honshu around 16 million years ago due to changes in the topography due to tectonic deformation and volcanic activity, and around 2 million years ago, the ground began to collapse due to compressive kinetic energy in the ocean floor. It is thought that the area rose to its current shape, with the Osado Mountains and Kosado Hills sandwiching the Kuninaka Plain. Uplift continues to this day due to tectonic movements such as earthquakes.

With a long history, Sado Island has been inhabited by humans for 10,000 years. Thousands of ruins discovered in the Kanai area included stoneware and hunting equipment from the late Yayoi period. There are also records of Sado in the Kojiki and Nihongi. After the Taika Reform, the central government established the Sado Province on the island, and the local population began to emigrate to Sado Island. At the same time, Sado Island has also become the place where losers of political conflicts or dissidents were exiled. Emperor Juntoku, Nichiren and other people had been exiled to Sado. After the Kamakura period, the Honma clan was appointed as the Shugodai. After 1589 ( Tenshō 17), Uesugi Kagekatsu invaded Sado Island, after which Sado Island was dominated by the Uesugi clan.

In 1601, miners discovered veins of gold and silver in the Aikawa Tsuruko Ginzan, which became the Sado Mine. In 1603 (Keichō 8), Tokugawa Ieyasu classified Sado Island as a territory of the Bakufu immediately after his victory at the Battle of Sekigahara. Sado Mine developed into the largest goldmine in Japan. Its output reached 41 tons by the Bakumatsu period in the mid-19th century, and it played an important role in the financing of the Shogunate. After the middle of the Edo period, the quantity began to decrease, but output rose to the highest level ever, at 400 kg a year, thanks to the introduction of advanced excavation technology during the Meiji era in the late 19th century. Sado Gold Mine closed in 1989. In nearly 400 years of mining history, it produced 78 tons of gold and 2,300 tons of silver.